refactor(ui): audit-pass fixes + dead-code/redundancy cleanup

Fixes from a full ui-new audit (OLED + e-ink both build green):
- remove dead DisplayDriver::drawScrollArrows (all lists use drawScrollIndicator)
- SettingsScreen selection bar -> lineStep()-1, matching the drawList screens
- HomeScreen: don't force the 1s blink refresh on the CLOCK page (status icons
  are hidden there anyway)
- FullscreenMsgView: clamp KEY_DOWN scroll to a cached _max_scroll instead of
  over-incrementing and leaning on the next render to clamp
- DataStore: clamp use_lemon_font (>1 -> 0) on load, like the other enum fields
- move the ~1.5KB wrap scratch (trans/lines) off the render stack into shared
  file-scope statics in FullscreenMsgView (single-threaded UI; the fullscreen
  view and history list never lay out in the same frame)

Cleanup:
- drop dead members RingtoneEditorScreen::DUR_VALS and HomeScreen::sensors_scroll
- delete redundant manual scroll-clamps in handleInput across the drawList
  screens (drawList already reclamps each render); remove the now-unused _visible
  from QuickMsgScreen/NearbyScreen/BotScreen and BotScreen::scrollToSel()

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/WaypointsView.h

@@ -319,7 +319,8 @@ public:
     int n = wpListCount();
     int total = n + 1;                       // + the "Add by coords" row
     if (c == KEY_CANCEL) { _mode = OFF; return true; }
-    if (c == KEY_UP   && _sel > 0)         { _sel--; if (_sel < _scroll) _scroll = _sel; return true; }
+    // drawList() reclamps _scroll from _sel every render.
+    if (c == KEY_UP   && _sel > 0)         { _sel--; return true; }
     if (c == KEY_DOWN && _sel < total - 1) { _sel++; return true; }
     if (c == KEY_ENTER) {
       if (_sel == n) openAddForm();          // last row → open the add form